2.1.3 - Karyotypes

DNA

The molecule that stores genetic information; typically a double helix of nucleotides with base pairs A–T and C–G.

Karyotype

A visual representation of the chromosomes of a cell, showing the full set for a species.

Diploid (2n)

Cells containing two complete sets of chromosomes; in humans, somatic cells are diploid (2n = 46).

Haploid (n)

Cells containing a single set of chromosomes; human gametes are haploid.

Somatic cell

A body cell that is diploid and not a gamete.

Sex cell (gamete)

A reproductive cell (sperm or egg) that is haploid.

Autosomal chromosome

Any chromosome numbered 1–22, excluding the sex chromosomes.

Sex chromosome

The X and Y chromosomes that determine biological sex in humans.

Banding

Staining patterns on chromosomes that reveal regions and help distinguish different chromosomes.

Base pairs

Paired nucleotides (A–T and C–G) that form the rungs of the DNA double helix.

46 (2n=46)

The diploid number of human somatic cells.

XX

Female sex chromosome complement in humans (two X chromosomes).

XY

Male sex chromosome complement in humans (one X and one Y).

Aneuploidy

Abnormal number of chromosomes in a cell (not an exact multiple of the usual set).

Trisomy

A condition where a cell has three copies of a chromosome (e.g., trisomy 21 in Down syndrome).

Monosomy

A condition where a cell is missing one chromosome from a pair.

Down syndrome (Trisomy 21)

A chromosomal disorder caused by three copies of chromosome 21.

Patau syndrome (Trisomy 13)

Three copies of chromosome 13.

Edwards syndrome (Trisomy 18)

Three copies of chromosome 18.

Klinefelter syndrome (47, XXY)

Sex chromosome aneuploidy in males with an extra X chromosome.

Turner syndrome (45, X)

Sex chromosome monosomy in females with only one full X chromosome.

Autosomes

Chromosomes 1–22 that are not sex chromosomes.